Yarn clamping mechanism

ABSTRACT

The clamping mechanism is provided with a stop member against which the clamp arms abut upon closing of the jaws. The stop member and arms are dimensioned so that a fraction of the spring force biasing the arms closed is absorbed by the stop member. The stop member can be mounted on the bearer member carrying the clamp or on the clamp arms. Also, the stop member can be of various geometric forms.

United States Patent [1 1 Pfarrwaller 1 Jan. 23, 1973 1 YARN CLAMPINGMECHANISM [75] Inventor: Erwin Pfarrwaller, Winterthur,

Switzerland [73] Assignee: Sulzer Brothers Ltd., Winterthur,

Switzerland [22] Filed: May 14, 1971 [21] App1.No.: 143,530

[30] Foreign Application Priority Data May 29, 1970 Switzerland..8055/7O [52] U.S. Cl ..l39/l25 [51] Int. Cl. ..D03j 5/06 [58] Field ofSearch ..139/l22 N, 125, 126, 127 R [56] References Cited UNITED STATESPATENTS 10/1969 Schneider ..l39/l26 Pfarrwaller 139/126 Darash ..139/125FOREIGN PATENTS OR APPLICATIONS 1,216,556 11/1959 France 139/125 PrimaryExaminer-Henry S. Jaudon Atmmeyl(enyon & Kenyon Reilly Carr & Chapin[57] ABSTRACT The clamping mechanism is provided with a stop memberagainst which the clamp arms abut upon closing of the jaws. The stopmember and arms are dimensioned so that a fraction of the spring forcebiasing the arms closed is absorbed by the stop member. The stop membercan be mounted on the bearer member carrying the'clamp or on the clamparms. Also, the stop member can be of various geometric forms.

13 Claims, 15 Drawing Figures "ll-Ill PATENTEDJM 23 1973 SHEET 1 [IF 3YARN CLAMPING MECHANISM This invention relates to a yarn clampingmechanism and, more particularly, to a yarn clamping mechanism for aweaving machine.

Yarn clamping mechanism have been known to consist of a carrier member,a yarn clamp which is fitted into the carrier member, is closable undera spring force and carries a pair of clamp jaws, and an opener fortemporarily opening the clamp jaws. Generally, these yarn clampmechanism have been used in widely varying textile machines in which ayarn or filament has to be engaged and brought into a specific positionduring operation of the machine, or when a specific movement has to beperformed with such yarn or the like. For example, clamping mechanismsof this type have been used in the weft yarn feeder of pickingmechanisms of gripper shuttle weaving machines (for example, inaccordance with one of the US. Pat. Nos. 2,845,095 or 2,728,359). Theseyarn feeders have served to feed to the gripper shuttle, the weft yarnend which is required to be inserted into the shed on the next pickingoperation, and to transfer the yarn end to a clamping mechanismoperating on a similar principle and incorporated in the gripper shuttle(for example in accordance with one of U.S. Pat. Nos. 2,660,201 and3,472,286). In these cases, immediately after a picking operation andshedding, the yarn feeder engages the picker-side end of the weft yarnwhich has just been drawn from the bobbin (which remains outside theshed during the picking operation) and which has just been introducedinto the shed. The length of yarn already introduced between the feederand the edge yarn clamp is then cut off from the next yarn a fewmillimeters ahead of the weft edge yarn clamp. For the remainder of theweaving operation, the new weft yarn end held by the feeder is returnedby the feeder in the direction towards the bobbin as far as the place atwhich this weft yarn end is taken over for the next picking operation byanother shuttle clamp which has been prepared in the picking mechanism.A yarn tensioner ensures that the weft yarn remains tensioned duringthis return movement.

To ensure a reliable transfer of the yarn end from the feeder clamp tothe shuttle clamp, the feeder has to introduce the yarn end veryaccurately into the open shuttle clamp. To this end, in the knownconstructions, the position of the clamp jaws when the feeder clamp isclosed is determined in relation to the gripper shuttle clamp by aseparate stop on which one of the two clamp arms of the feeder which isunder somewhat stronger spring biasing than the other is operativelysupported. The other weaker clamp arm does not have such a stop or thelike, so that the spring tension operative thereon acts fully as aclamping force between the clamping jaws and serves to hold the yarn.The construction andarrangement of the feeder clamp are thus notsymmetrical with respect to the path of the yarn. The direct adjustmentof a yarn clamp of this kind is relatively complex.

The clamping force by which the clamping jaws are pressed against oneanother is selected according to the nature of the weft yarn to beintroduced and according to the picking speed in order, first, to ensurereliable retention of the yarn in the clamp (no yarn losses or minimumyarn losses), and, second, to prevent damage to the yarn clamped betweenthe jaws. The yarn tension I brakes and yarn tensioners during andbetween consecutive picking operations is also adjusted to differentdegrees according to the yarn quality and picking speed in order toavoid unnecessary stress on the yarn and yet keep the yarn uniformlytaut during all stages of the weaving operation.

In practice it has been found that vibration occurs at individualelements of the known yarn clamping mechanisms, more particularly theclamp arms, clamp jaws and springs, during operation and such vibrationis caused partly by the rapid opening and closing of the clamps underthe control of the clamp opener, and partly by the movements of thebearer member (the yarn feeder arm or shuttle member) and in some casesby other external influences operative during the picking operation (forexample, the guidance of the shuttle as it passes through the shed).Such vibration has an adverse effect on the operational reliability ofthe yarn clamp since it produces clamp jaw rebound and abrasion or atleast favors the same. To ensure adequate reliability against yarnlosses, it is therefore necessary for the clamping force by which thejaws are pressed into contact to be adjusted to a relativelyconsiderable value, for example of the order of 2.2 kg and more foraverage yarns and picking speeds of about 15 to 20 meters per second.This is more than would be required to retain the yarn, if it were notnecessary to allow for the clamp vibration.

Accordingly, it is an object of the invention to improve the operationof a yarn clamp by preventing or at least greatly reducing the vibrationof the clamp arms and clamp jaws.

It is another object of the invention to provide a symmetric yarnclamping mechanism.

It is another object of the invention to provide for a reliable andsmooth transfer of a yarn between a yarn feeder and a shuttle.

Briefly, the invention provides a yarn clamping mechanism which isconstructed of a yarn clamp having a pair of spring-biasedjaw-supporting clamp arms with at least one stop member having stopsurfaces upon which the clamp arms bear with a fraction of the springforce when the clamp is closed.

The stop member may be made from a material which is not itself veryresilient, for example wood or metal, but preferably at least partiallyis made from a material which is flexibly resilient with a dampingaction, for example rubber or plastics.

It has been found by experience that the occurrence 'of vibration of theclamp arms, springs and clamp jaws can be extensively obviated byappropriate adjustment of the contact pressure between the clamping armsand the stop surfaces and selection of the material used for the stopsurfaces and by suitable shaping of the stop member, clamp arms andsprings.

With this arrangement, and without adversely affecting security againstyarn losses, and under otherwise identical conditions, the spring forceacting on the clamp jaws can be appreciably reduced as compared with theknown clamping mechanisms, and by as much as one third in certain cases.Since the clamp jaws rebound on one another to a lesser extent and nolonger rub on one another in the closed condition, the yarn end clampedtherebetween is not treated as rigorously and the life of the clampingmechanism is increased accordingly.

Conversely, the construction of the yarn clamping mechanism according tothe invention offers the possibility of achieving greater operationalreliability of the weft introduction than with the known constructions,

for the identical clamping force acting on the jaws, i.e.,

the clamping mechanism can be used for weaving machines having greaterweaving widths and/or for higher picking speeds or accelerations thanwithout vibration-damping stops.

The invention can be embodied with various known forms of constructionof clamp arms, stop members and springs. For example, the stop membercan be used with a yarn feeder which is constructed with rigidspring-loaded clamp arms pivotally connected to a carrier member attheir ends remote from clamp jaws at the free ends. This form of yarnclamp has the advantage of a relatively strong stable construction inwhich the jaws are guided in exact parallel relationship to one anotherin every position and cannot twist relatively to one another, even ifthe yarn does not lie exactly in the axis of symmetry of the clamp jaws.

Also, the stop member can be used in a gripper shuttle clamp wherein apair of clamp arms are constructed as prestressed spring arms and arerigidly connected to a carrier member at their ends remote from theclamp jaws at the free ends. The two clamp arms may then be made in onepiece, i.e., the arms can be interconnected by a yoke in the form of a Uat their ends remote from the clamp jaws, the yoke being secured, forexample as by riveting, to the carrier member. This type of clamp isvery simple and light, and insensitive to impacts and vibrations due toexternal influences.

In one embodiment, the stop member is secured to the carrier member ofthe yarn clamping mechanism. The stop member is then able to provide acertain guidance and centering for the yarn clamp so that the spatialposition of the clamp jaws in their closed condition is clearly definedin relation to the carrier member. Thus, for example, in the case of ayarn feeder it is no longer necessary, as is the case with the knownconstructions, to make the two clamp arms of different thicknesses,subject them to different prestressing and provide the more biased armwith a fixed stop. On the contrary, the clamp can be completelysymmetrical thus greatly simplifying stock-keeping of component partsand allowing the finished clamp to be adjusted. Also, centering of theclosed clamp ensures a perfect transfer of the yarn, for example fromthe feeder to the shuttle clamp.

. In a gripper shuttle with a stop member secured to the carrier memberand disposed between two clamp arms, the clamp simply requiressecurement by a single rivet instead of two rivets as previouslyrequired in the to the carrier member for structural reasons, the stopmember can be secured to a clamp arm.

In another embodiment, instead of one stop member disposed between theclamp arms, two stop members may be provided outside a pair of actuatinglevers for the clamp arms with the levers bearing against the stopmembers when the clamp is closed.

The resilience of the stop surfaces against which the clamp arms bear onthe stop member when the clamp is closed is advantageously dimensionedaccording to the yarn quality to be picked and the proposed pickingspeed (or yarn acceleration). For example, on a changeover of a weavingmachine to different operating conditions or to a different yarnquality, both the yarn feeder and the shuttles can be interchanged forthose in which the yarn clamps and stop members are found to beparticularly suitable for the conditions applying to the next weavingoperation.

In further embodiments of the yarn clamping mechanism according to theinvention, the distance between the stop surfaces on the stop memberassociated with, i.e., simultaneously operative on, the two clamp armsis adjustable. The clamping mechanism may also be adapted to receivestop members which have different distances between the stop surfacesassociated with the two clamp arms and which can be turned intodifferent positions or be interchanged. Finally, the distance betweenthe stop member and clamp jaws as measured in the longitudinal directionof the clamp may be adjustable. It is thus possible to vary the lengthof the effective lever arm by which the clamp arms are pressed on to thesupporting surfaces. In practice, this has the same effect as avariation in the resilience of a stop member mounted rigidly on thebearer member.

These and other objects and advantages of the invention will become moreapparent from the following detailed description and appended claimstaken in conjunction with the accompanying drawings in which:

FIG. 1 illustrates an embodiment of a clamping mechanism according tothe invention as used in a yarn feeder mechanism comprising two rigidclamp arms with the yarn clamp closed;

FIG. 2 illustrates a plan view of the yarn clamp according to FIG. 1 inpartial section on the line II-II in FIG. 1;

FIG.v 3 illustrates an elevation of the yarn clamp shown in FIG. 1 withthe clamp open;

FIG. 4 illustrates a sectional view of the yarn clamp taken on line IVIVof FIGS;

FIG. 5 illustrates an elevational view of a gripper shuttle with a yarnclamp mechanism according to the invention wherein the clamp arms areconstructed as spring arms;

FIG. 6 illustrates a plan view taken on line VI -VI of FIG. 5 of theshuttle;

FIG. 7 illustrates an elevational view of the cylindrical stop memberprovided with damping stops as shown in FIG. 5;

FIG. 8 illustrates a partial sectional view through a gripper shuttlesimilar to FIG. 5 but with a different embodiment of the stop membersecured to a clamp arm;

FIG. 9 illustrates a view taken along line IX-IX of FIG. 10 of a grippershuttle similar to FIG. 6 but with a stop member having adjustableresilience;

FIG. illustrates a view taken on line X-X of FIG.

FIGS. 11 and 12 are'two similar views of FIGS. 3 and 4 but with anaxially adjustable stop member, those parts which are the same as FIGS.3 and 4 having been omitted;

FIGS. 13 and 14 are a section and elevation similar to FIGS. 9 and 10but with a stop member of hexagonal cross-section; and

FIG. illustrates a diagrammatic view of a stop member of ovalcross-section.

Referring to FIGS. 1 to 4, the carrier member 1 for a weft yarn feederis in the form of a profiled rail which is displaceable forward and backas a unit in the direction of the arrow 3 in manner known per se toengage and guide a weft yarn 2 or a weft yarn end. The carrier member 1mounts a clamp therein which is constituted by a pair of clamp jaws 4situated at the free ends of a respective pair of rigid clamp arms 5which, at their ends remote from the clamp jaws 4, are pivotallyconnected to the carrier member 1 by pivots 6. The clamp arms 5 areextended, beyond the bores surrounding the pivots 6, in the form ofactuating levers 7 into which a hard metal plate 8 is recessed at theplace at which a fork-shaped opener 9 meets the actuating levers 7 toopen the clamp when the opener 9 moves transversely of the plane of thecarrier member 1 in the direction of the arrow 10. Two spring arms 11,which at one end are rigidly secured to the carrier member 1 by rivetsl2, exert an outwardly directed spring force on the actuating levers 7at their free ends so that the levers 7 are formed apart and the jaws 4are pressed towards one another as long as the opener 9 is in a rearwardinoperative position out of engagement with the actuating levers 7. Ifthe opener 9 is pushed forward into an operative position, a pair ofinner surfaces 13 of the fork-shaped opener 9, which converge in theform of a wedge, strike the hard metal plates 8 in the actuating levers7 and press the levers 7 together. The clamp arms 5 are thus pivotedabout their pivots 6 so that the clamp opens until the actuating levers7 bear against a limiting stop 14 secured within the carrier member 1 asshown.

A stop member 15 is secured, for example by a rivet, in the carriermember 1 between the clamp arms 5 and consists of a material which isitself solid, for example wood or metal, or preferably at least partlyof a material which is resiliently flexible with a damping action, forexample, rubber or a plastic such as Nylon, Teflon, or

' the like. The stop member 15 also has damping stop surfaces 16 onwhich the spring-biased clamp arms 5 bear by a fraction of the springforce operative thereon, when the clamp is closed, the remaining springforce serving to press the jaws 4 together, (i.e., to engage the yarn 2.The contact pressure by which the jaws 4 are pressed against one anotheris freely selectable or adjustable within wide limits on the basis ofempirical values and depends on the properties of the yarn 2 used, suchas, the yarn diameter, weight, strength, elasticity, etc. In thisembodiment, the contact pressure is determined by the shape and theadjustment (for example, by subsequent cold deformation) of the springarms 11, and by the position, shape and resilience of the stop member15. If required, the stop member 15 is compressed by an amount x at thestop surfaces 16 by the clamp arms 5 as a result of the inherentresilience thereof when the clamp is closed. When the clamp is opened,the stop member 15 resumes its original shape, for example, acylindrical shape, owing to the elasticity thereof. When the clamp isopen, there is no longer any contact between the arms 5 and the dampingsurface 16.

The shape and dimensions of the clamp arms 5, the actuating levers 7, 8and the spring arms 11, and the biasing of the spring arms 11 influencethe type of oscillations or vibrations which experience has shown wouldoccur in operation without the stop member 15 at the individual elementswhen the clamp is actuated by the opener 9 or as a result of otherexternal effects. The dimensions, the shape and the mechanicalproperties of the stop member 15 and of the clamp arms 5 determine theefficiency, more particularly the damping properties, ofthe clampingmechanism according to the invention.

Referring to FIG. 1, the stop member 15 can alternatively be replaced bya pair of stop members 15a each of which is provided on each of twocross-members 1a, 1b of the carrier member 1 with the respective one ofthe actuating levers 7 bearing there against when the clamp is closed.These stop members 15a are also of a material and a construction to beresiliently flexible with a damping action.

The yarn feeder or the yarn clamping mechanism shown in FIGS. 1 to 4 isof completely symmetrical construction with respect to the yarn path. Inorder to obtain a satisfactory transfer of the yarn end from the feederto a shuttle clamp, it is important that the jaws 4 in the closedcondition, i.e., with the yarn end held therein, should be in anaccurately determined position immediately adjacent the open shuttleclamp at the moment of transfer. This is achieved with a substantiallyplay-free accurate guidance of the carrier member 1 in the weavingmachine picking mechanism (not shown), by the fact that thespring-biased clamp arms 5 pivot freely about their pivots 6 closearound the stop member 15 and bear against the stop surfaces 16 on bothsides. The stop member 15 thus centers the closed clamp and holds theclamp, together with the yarn end held thereby, exactly in the requiredposition with respect to the carrier member 1 and hence to the grippershuttle clamp.

Referring to FIGS. 5 to 7, the yarn clamping is incorporated into aweaving machine gripper shuttle which cooperates with a weft yarn supplybobbin remaining outside the shed during picking. The carrier member isin the form of a sleeve 21 of a one-piece or multi-part shuttle memberof conventional construction. At the front, i.e., in the pickingdirection, the shuttle member sleeve 21 comprises a solid head 22 and,at the rear, an opening 23 through which the yarn clamp 24, 25, 31 isintroduced and installed in the shuttle. A slot-shaped opening 27 isalso formed in the rear end of the sleeve 21 with the jaws 24 disposedin the region of the opening so that the jaws 24 are accessible but areprotected from external influences. The clamp arms 25 are in the form ofprestressed spring arms and are reinforced by thickened portions or hardmetal plates 28 which are aligned with bores 26 in the side walls of thesleeve 21. The bores 26 permit passage of a clamp opener 29 whichpresses against the thickened portions 28 via a wedge-shaped edge 33during movement forward and back in the direction of the arrow 30, toopen the arms 25 and hence the jaws 24, i.e., the clamp. The two springarms 25 are interconnected by a yoke 31 and is made in one piece. Theyoke 31, in turn, is secured to the carrier member (sleeve 21) forexample, by means of a rivet 32. A substantially cylindrical stop member35 (FIG. 7) of a diameter 39 which is solid or, if required, resilientlyflexible with a damping action, is pressed or riveted into another bore34 in the sleeve 21 having a stepped diameter and forms a damping stopsurface 36 for each of the spring arms 25. When the clamp is closed, thestop surface 36 can be pressed in by the amount x, if the surface 16 isof resilient construction. Here again, the stop member 35 centers theclamp with respect to the axis of symmetry of the shuttle so that asingle rivet 32 is sufficient to fix the clamp in the shuttle member.With such a construction, given the same overall length of the shuttle,it is possible to incorporate longer spring arms 25 in the shuttle thanin the case of the previously convehtional forms in which the yoke 31 ofthe clamp is secured to the shuttle member by two consecutively disposedrivers.

In the two previously described embodiments, the stop member is securedto the carrier member in any desired manner, for example riveted,screwed, pressed in or glued. If a seperable connection is required, thedamping properties can be adjustable to a certain degree to adaptto therequirements of different types of filaments or yarns, for example, byproviding in terchangeable stop members 15, 35 which has differentdistances widths over flats between their opposite stop surfaces 16.

Instead of being constructed as a cylinder of round cross-section, thestop member may also be cube shaped 37 and may be secured to one of theclamp arms 25 so as to have one stop surface 38 (FIG. 8). Also, the stopmember can be in the form of a hexagon 35b (FIGS. 13 and 14), octagon,etc. and can be provided with a spacer bush 41b so as to benon-compressi ble in the longitudinal direction. These members, asshown, can be secured to the sleeve 21 by a counter sunk screw 42b.Advantageously, members are then used which have widths over flats? 39a,39b, 390 which differ slightly (by a few tenths of a millimeter) betweeneach pair of opposite stop surfaces, i.e., simultaneously operative stopsurfaces, so that where necessary, the member can be turned to adifferent widths over flats 39a, 39b, 390 for the purposes of adaptingthe damping properties. Continuous adjustability can be obtained byusing a stop member 350 (FIG. having a slightly oval cross-section,which is adapted to turn about its axis in the direction of the arrow 46and be secured in the bearer member 1 by a suitable bush 41c andcountersunk screw 420 for the spacer bush 41c.

Referring to FIGS. 9 and 10, a resilient stop member 35a is ofcylindrical construction in comparison with 35b in FIG. 13 and can becompressed in its longitudinal direction transversely of the sleeve 21by a pressure plate 41 and a countersunk screw 42 so that the diameter39 and resilience thereof are adjustable with respect to the clamp arms25 within certain limits according to the required purpose.

Referring to FIGS. 11 and 12, wherein like reference characters indicatelike parts as above, the stop member consists of a rigid metal block 43and, if required, is provided with stop buffers 44 which are flexiblyresilient with a damping action. These buffers 44 have flat stopsurfaces which are spaced apart by a distance 39 as above described. Theblock 43 is guided in a longitudinal slot 45 of the carrier member 1 byappropriately constructed guide edges and is clamped adjustably in thelongitudinal direction by means of a screw 42a with a washer. In thisway, the distance 40 between the jaws 4 and the stop member 43, 44,i.e., the length of the clamp arm lever operative for the stop, can beadjusted as required.

What is claimed is:

1. A yarn clamping mechanism comprising a carrier member;

a yarn clamp mounted in said carrier member and having a pair of springbiased arms therein and a jaw on each said arm;

at least one resilient and damping stop member having stop surfacesthereon for temporarily engaging each of said arms with a fraction ofthe spring force with said jaws closed on each other and being spacedfrom said arms with said jaws opened with respect to each other; and

an opener for temporarily opening said jaws.

2. A yarn clamping mechanism as set forth in claim 1 wherein each saidarm is rigidly constructed and pivotally connected to saidcarrier memberat an end remote from said jaws thereon.

3. A yarn clamping mechanism as set forth in claim 1 wherein each saidarm is a prestressed spring arm rigidly connected to said carrier memberat an end remote from said jaw thereon.

4. A yarn clamping mechanism as set forth in claim 3 wherein said armsare integrally connected together in a one-piece member.

5. A yarn clamping mechanism as set forth in claim 1 wherein said stopmember is secured to said carrier member.

6. A yarn clamping mechanism as set forth in claim 1 wherein said stopmember is secured to one of said arms.

7. A yarn clamping mechanism as set forth in claim 1 wherein said stopmember has a plurality of stop surfaces thereon, each pair of oppositelydisposed stop surfaces being spaced apart a distance different from theremaining pairs of oppositely disposed stop surfaces.

8. A yarn clamping mechanism as set forth in claim 1 wherein said stopmember has a oval shaped stop surface.

9. A yarn clamping mechanism as set forth in claim 1 1 wherein said stopmember is adjustably mounted with.

being resiliently compressible to deform under engagement with saidclamp arms.

13. The combination as set forth in claim 12 wherein said clamp arms areintegrally connected to each other to form a U-shaped member and saidstop member is mounted intermediately between said arms.

1. A yarn clamping mechanism comprising a carrier member; a yarn clampmounted in said carrier member and having a pair of spring biased armstherein and a jaw on each said arm; at least one resilient and dampingstop member having stop surfaces thereon for temporarily engaging eachof said arms with a fraction of the spring force with said jaws closedon each other and being spaced from said arms with said jaws opened withrespect to each other; and an opener for temporarily opening said jaws.2. A yarn clamping mechanism as set forth in claim 1 wherein each saidarm is rigidly constructed and pivotally connected to said carriermember at an end remote from said jaws thereon.
 3. A yarn clampingmechanism as set forth in claim 1 wherein each said arm is a prestressedspring arm rigidly connected to said carrier member at an end remotefrom said jaw thereon.
 4. A yarn clamping mechanism as set forth inclaim 3 wherein said arms are integrally connected together in aone-piece member.
 5. A yarn clamping mechanism as set forth in claim 1wherein said stop member is secured to said carrier member.
 6. A yarnclamping mechanism as set forth in claim 1 wherein said stop member issecured to one of said arms.
 7. A yarn clamping mechanism as set forthin claim 1 wherein said stop member has a plurality of stop surfacesthereon, each pair of oppositely disposed stop surfaces being spacedapart a distance different from the remaining pairs of oppositelydisposed stop surfaces.
 8. A yarn clamping mechanism as set forth inclaim 1 wherein said stop member has a oval shaped stop surface.
 9. Ayarn clamping mechanism as set forth in claim 1 wherein said stop memberis adjustably mounted with respect to said jaws.
 10. A yarn clampingmechanism as set forth in claim 1 wherein said stop member is made atleast partially from a material which is resiliently flexible and has adamping action.
 11. A yarn clamping mechanism as set forth in claim 1wherein said stop surfaces are adjustable with respect to said arms tovary the distance therebetween.
 12. In combination with a yarn clampingmechanism having a pair of spring biased clamp arms, each of said armshaving a jaw mounted thereon in opposition to a jaw on the other arm; atleast one stop member having stop surfaces thereon for engaging saidarms under a fraction of the spring biasing force biasing said arm uponclosing of said jaws on each other, said stop member being spaced fromsaid arms upon opening of said jaws relative to each other and said stopsurfaces being resiliently compressible to deform under engagement withsaid clamp arms.
 13. The combination as set forth in claim 12 whereinsaid clamp arms are integrally connected to each other to form aU-shaped member and said stop member is mounted intermediately betweensaid arms.